Trimester-Specific Association of Maternal Exposure to Fine Particulate Matter and its Components With Birth and Placental Weight in Japan

Objective: We investigated which trimester of exposure to PM_2.5 and its components was associated with birth and placental weight, and the fetoplacental weight ratio. Methods: The study included 63,990 women who delivered singleton term births within 23 Tokyo wards between 2013 and 2015. Each day, we collected fine particles on a filter, and analyzed their chemical constituents, including carbons and ions. Trimester-specific exposure to each pollutant was estimated based on the average daily concentrations. Results: Over the third trimester, sulfate exposure tended to be inversely associated with birth weight, and decreased placental weight (difference for highest vs lowest quintile groups =- 6.7 g, 95% confidence interval = -12.5 to -0.9). For fetoplacental weight ratio, there was no relationship. Conclusions: Sulfate exposure over the third trimester may reduce birth weight, particularly placental weight.